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title: "20 UK Regional Build Over Agreement, Water Authority & Clay Soil Depth Hubs (2026) | BuildOverAgreement.co.uk"
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> **Canonical Source:** [https://buildoveragreement.co.uk/locations](https://buildoveragreement.co.uk/locations)
>
> *Check your local UK Water Authority, shrink-swell clay foundation trench depth, and Part H4 public sewer rules across 20 major regions in England and Wales.*



### Organization: BuildOverAgreement.co.uk (UK Drainage & Environmental Standards Desk)

| Field | Value |
| :--- | :--- |
| **Organization** | BuildOverAgreement.co.uk (UK Drainage & Environmental Standards Desk) |
| **Official Website** | https://buildoveragreement.co.uk |
| **Email** | compliance@buildoveragreement.co.uk |


### Entity: BuildOverAgreement.co.uk — UK Part H4 Sewer & Foundation Calculator

| Property | Detail |
| :--- | :--- |
| **Type** | WebSite |
| **Name** | BuildOverAgreement.co.uk — UK Part H4 Sewer & Foundation Calculator |


### Entity: BuildOverAgreement.co.uk Part H4 Compliance & Lintel CAD Calculator (2026)

| Property | Detail |
| :--- | :--- |
| **Type** | WebApplication |
| **Name** | BuildOverAgreement.co.uk Part H4 Compliance & Lintel CAD Calculator (2026) |


### Step-by-Step Procedure: How to Obtain a UK Build Over Agreement for an Extension (2026)

> **Objective:** Step-by-step statutory process under Building Regulations Approved Document H4 and Section 174 Water Industry Act 1991.

#### 1. Locate Public Sewer & Invert Depth

Consult your CON29DW drainage search or lift the inspection chamber cover to measure sewer distance, pipe diameter (100mm–300mm), and invert depth.

#### 2. Check 3.0m Trigger Zone & 45-Degree Load Cone

Verify whether your new extension foundation trench falls within 3.0m horizontally of the sewer or inside the 45-degree angle of repose from the pipe invert.

#### 3. Specify Foundation Depth & Bridging Lintel

Excavate foundations to at least sewer invert + 150mm, and span over or near the pipe using reinforced concrete lintels with 450mm end bearings and a 150mm compressible crown void former.

#### 4. Submit Free Self-Certification or Formal Dossier

Lodge your 1:20 cross-section, 1:100 site plan, and WRc MSCC5 CCTV drain survey with your statutory water undertaker and Building Control before pouring concrete.





Regional Ground & Sewer Directory

# 20 UK Regional Ground & Build Over Hubs

Local soil geology, shrink-swell clay foundation depths, and statutory water undertakers across England and Wales.

- **[London & Thames Valley](/locations/london-thames-valley)** — Greater London / Berkshire / SurreyDense Victorian combined brick-egg and vitrified clay sewers. Over 60% of residential extensions encounter shared lateral drains adopted in 2011.Authority: Thames WaterSoil: London Clay Formation overlying Lambeth Group sands and gravels. Extreme swelling and shrinkage characteristics.Fnd Depth: 1.5m
- **[Birmingham & West Midlands](/locations/birmingham-west-midlands)** — West MidlandsExtensive 1930s suburban housing stock with shared rear-garden drainage runs connecting multiple semi-detached properties into Severn Trent mains.Authority: Severn Trent WaterSoil: Mercia Mudstone Group with glacial sands and boulder clay deposits.Fnd Depth: 1.25m
- **[Manchester & Greater Manchester](/locations/manchester-greater-manchester)** — Greater ManchesterHigh rainfall runoff leading to combined sewer surcharging. Victorian terraced properties in Salford and Trafford feature shared back-alley lateral sewers.Authority: United UtilitiesSoil: Glacial Till and Sherwood Sandstone with localized peat pockets.Fnd Depth: 1.25m
- **[Leeds & West Yorkshire](/locations/leeds-west-yorkshire)** — West YorkshireHistorical back-to-back terraced properties with stone-slab culverts and shared earthenware drains regulated by Yorkshire Water.Authority: Yorkshire WaterSoil: Pennine Lower Coal Measures comprising sandstone, siltstone, and mudstone.Fnd Depth: 1m
- **[Bristol & Avon](/locations/bristol-avon)** — City of Bristol / SomersetSteep undulating topography creates high hydraulic heads in local foul drains. Wessex Water strictly enforces pre-build CCTV surveys.Authority: Wessex WaterSoil: Triassic Red Clays, Mercia Mudstone, and Carboniferous Limestone.Fnd Depth: 1.25m
- **[Sheffield & South Yorkshire](/locations/sheffield-south-yorkshire)** — South YorkshireFrequent encounters with deep Victorian stone sewers requiring structural engineered bridging details across steep valleys.Authority: Yorkshire WaterSoil: Carboniferous Sandstones and Siltstones with variable mining backfill.Fnd Depth: 1m
- **[Liverpool & Merseyside](/locations/liverpool-merseyside)** — MerseysideVictorian and Georgian sewer networks in inner suburbs with deep invert levels often requiring piled foundation bridging.Authority: United UtilitiesSoil: Sherwood Sandstone Group overlain by glacial sands and estuarine alluvium.Fnd Depth: 1m
- **[Nottingham & East Midlands](/locations/nottingham-east-midlands)** — NottinghamshireShallow sandstone bedrock combined with 1930s clay sewer runs. Severn Trent self-cert is common for standard extensions.Authority: Severn Trent WaterSoil: Chester Formation Sandstone and Mercia Mudstone.Fnd Depth: 1.25m
- **[Leicester & Leicestershire](/locations/leicester-leicestershire)** — LeicestershireExpansive clay soils prone to subsidence. Foundation depth often exceeds 1.5m, immediately triggering Section 6 Party Wall notices alongside H4.Authority: Severn Trent WaterSoil: Charmouth Mudstone Formation and Oadby Till member.Fnd Depth: 1.5m
- **[Coventry & Warwickshire](/locations/coventry-warwickshire)** — WarwickshirePost-war reconstruction housing estates with shared sewer branches running across multiple rear gardens.Authority: Severn Trent WaterSoil: Warwickshire Group mudstones and sandstones.Fnd Depth: 1.25m
- **[Cardiff & South Wales](/locations/cardiff-south-wales)** — South GlamorganDŵr Cymru Welsh Water mandates strict compliance with SuDS regulations and mandatory asset mapping verification.Authority: Dŵr Cymru Welsh WaterSoil: Mercia Mudstone and Alluvium deposits along the Severn Estuary plain.Fnd Depth: 1.25m
- **[Newcastle & Tyne and Wear](/locations/newcastle-tyne-wear)** — Tyne and WearMining influence zone requiring geotechnical assessment of foundation loads over Northumbrian Water infrastructure.Authority: Northumbrian WaterSoil: Pennine Middle Coal Measures overlain by dense glacial till.Fnd Depth: 1m
- **[Brighton & East Sussex](/locations/brighton-east-sussex)** — East SussexChalk groundwater protection zone. Southern Water enforces strict measures to prevent any sewage infiltration into aquifer strata.Authority: Southern WaterSoil: Chalk Formation of the South Downs with thin clay-with-flints topsoil.Fnd Depth: 1m
- **[Southampton & South Hampshire](/locations/southampton-hampshire)** — HampshireHigh coastal water tables and marine clay deposits. Deep foundations require engineered bridging lintels over shared sewers.Authority: Southern WaterSoil: Barton Clay and Bracklesham Group clays, silts, and sands.Fnd Depth: 1.5m
- **[Portsmouth & Solent](/locations/portsmouth-solent)** — HampshireIsland geography with high water table and pumped sewer networks. Building over rising mains is categorically banned.Authority: Southern WaterSoil: River Terrace Deposits and marine gravels on Portsea Island.Fnd Depth: 1m
- **[Reading & Berkshire](/locations/reading-berkshire)** — BerkshireFast-track Thames Water self-certification heavily utilised by homeowners building rear kitchen extensions.Authority: Thames WaterSoil: Thames Valley alluvial gravels overlying London Clay and Chalk.Fnd Depth: 1.5m
- **[Milton Keynes & Buckinghamshire](/locations/milton-keynes-buckinghamshire)** — BuckinghamshireNew-town masterplanned drainage where public sewers run through private back gardens under early Anglian Water transfer agreements.Authority: Anglian WaterSoil: Oxford Clay Formation and Kellaways sand members.Fnd Depth: 1.5m
- **[Cambridge & Cambridgeshire](/locations/cambridge-cambridgeshire)** — CambridgeshireHighly reactive clay causing seasonal ground heave and shrinkage. Piled foundations near sewers are standard requirement.Authority: Anglian WaterSoil: Gault Clay Formation with Fenland alluvium and peat fringes.Fnd Depth: 1.5m
- **[Norwich & Norfolk](/locations/norwich-norfolk)** — NorfolkVast rural and semi-urban catchment where surface water soakaways and public sewers intermingle.Authority: Anglian WaterSoil: Crag Group sands, gravels, and Lowestoft Formation boulder clay.Fnd Depth: 1.25m
- **[Exeter & Devon](/locations/exeter-devon)** — DevonRed sandstone bedrock with steep topography. South West Water requires rock excavation assessments for trenching.Authority: South West WaterSoil: Exeter Group breccias, sandstones, and Devonian mudstones.Fnd Depth: 1m

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